This invention relates to die cutter blankets used to cover anvils in a sheet material die cutting apparatus.
Die cutter blankets are thermoset molded urethane material that wrap about steel circular cylindrical anvils. The anvils typically have a channel in the surface thereof extending along the anvil longitudinal axis. The blankets are wrapped about the anvil and have locking projections in some embodiments. The blankets are sheet material with opposing end edges at which the locking projections are located. The ends are complementary and the locking projections engage when inserted into the channel. The locking projections interlock when inserted into the anvil channel, locking the edges to the blanket, locking the blanket to the anvil and preclude the blanket from rotating about the anvil.
U.S. Pat. No. 3,765,329 discloses one aspect of a blanket with such projections. The plastic blanket has a sheet metal inner liner. The locking projections form a two part snap in construction in which a female part receives a male part, the female part depending from the blanket at one end edge thereof with a longitudinal rounded groove and the male part is complementary to the groove and snaps into the groove. The male part may be made of metal. The female part has a metal support. The male and female parts depend from the blanket edge for insertion into the anvil channel.
Other complementary locking structures are shown in U.S. Pat. Nos. 4,848,204, 3,885,486, 4,867,024, 5,078,535 and 5,758,560. All of the above patents use inerlocking complementary depending structures which fit into the anvil channel and cooperate with each other and the anvil channel to lock the blanket ends together.
Another locking arrangement for locking blanket ends together employs interlocking interdigitated fingers which are somewhat dovetail in shape. U.S. Pat. Nos. 4,075,918, 4,791,846 and 3,577,822 disclose this type of interlocking arrangement for use with a die cutter blanket. The interlocking fingers are in the same plane as the blanket sheet material and overlie the anvil. The anvil has a channel. The interlocking fingers, in some embodiments, may overlie the channel. The blanket interlocking finger end portions or other portions of the blanket have a depending projection which fits within the anvil channel to preclude the blanket from rotating relative to the anvil. The blanket is generally of uniform thickness except for the depending projections which add considerable thickness to the blanket at the anvil channel. The blanket is formed of molded urethane and in some embodiments is supported by a woven nylon or fiberglass fabric. The blanket thus comprises two materials, urethane forming the blanket structure and the support woven fabric to which the blanket is molded.
A problem with this construction is that the blanket eventually exhibits a recessed flat portion over the anvil channel during use. This recessed flat portion creates a problem with the product die cut by the apparatus. The die cutters cut into the sheet material being die cut, typically corrugated or pressed cardboard. The cutters also cut somewhat into the blanket. Because of the resiliency of the blanket material the blanket wears uniformly except at the anvil channel and depending projection which results in the recessed flat portion. Because of this recess flat portion, the dies eventually do not cut uniformly through the blank sheet material at this location causing the premature production of poor product. The recessed portion does not permit the dies at this location to cut cleanly through the product sheet material.
The present inventor attributes the recessed flat portion to the greater thickness of the urethane material at the projection region depending into the anvil channel. The present inventor recognizes the source of the problem not heretofore recognized by those of ordinary skill in this industry. The present inventor believes that since the material is resilient, the thicker material at the anvil channel exhibits non-linear increasingly greater resiliency than the sheet blanket material over the rest of the anvil. The present inventor believes that this greater resiliency results in excessive wear of the blanket material at this location as compared to the rest of the blanket surface. That is, the die cutters cut away more material from the blanket at this location than in the rest of the blanket for a given time period of use due to the increased resiliency of the material at the anvil channel region. This problem is only present with the interlocking finger construction which uses solid urethane material at the anvil channel.
According to the present invention, the above problems are minimized by a die cutter blanket for use with an anvil having an axially extending channel in the surface thereof comprising a urethane sheet member blanket having first and second ends, the blanket for wrapping about the anvil. A plurality of complementary interlocking fingers are at the first and second ends for selective interlocking engagement with each other to secure the blanket to the anvil. A first projection depends from and is integral one piece with the sheet member blanket of the same material as the blanket at at least one of the ends for complementary engagement with the channel, the material forming the projection and blanket having a first given property such that the blanket exhibits excessive surface wear at the first projection during use in comparison to the rest of the blanket surface unless otherwise precluded. An insert is embedded in the blanket at at least one of the ends overlying at least the first projection, the insert having a second given property different than the first given property for substantially precluding the excessive wear.
In one aspect the insert is urethane and in another aspect the insert forms a portion of the fingers.
In a further aspect, the insert is sheet material with a second projection depending therefrom forming a portion of the first projection.
In a further aspect, a woven sheet support member is included to which the blanket is secured.
In a further aspect, the insert has a plurality of through bores, a portion of the material of the blanket being embedded in the through bores.
Preferably, the through bores have a chamfered end region.
In a further aspect, the support member has a depending portion extending into the first projection from the plane of the support material.
Preferably, the blanket has a working surface for facing the cutting dies, the support member being uniformly spaced from the working surface of the blanket throughout the blanket.
Preferably the insert is a sheet member. In a further aspect, the sheet member has a projection depending therefrom. Preferably, the sheet member insert is approximately rectangular in plan view having opposing end edges and lateral opposing edges, the projection extending transversely across the sheet member medially the end edges to the opposing lateral edges.
In a further aspect, the blanket first property is a durometer of about 85 and the insert second property is a durometer of about 90
In a still further aspect, the first and second properties are the values of cut and tear resistance of the material wherein the blanket exhibits less resistant to cut and tears than the insert for a given load thereon.
In a further aspect, the first and second properties are the values of rebound of the material wherein the blanket exhibits a higher rebound value than the insert.
In a further aspect, the first and second properties are the modulus values of the material wherein the blanket exhibits a higher modulus than the insert.